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Protection of low voltage interface against ESD, EFT, and surge

Kaveh Mohammad
Intellectual 585 points

Other Parts Discussed in Thread: ESD341, ESDS304, ESDS302, ESDS314, ESDS312, TSD05, TVS0500

Hi, 

I have an ethernet port and a serial RS232 interface in my design that I am trying to protect against ESD, EFT, and surge to comply with IEC 61000-4-2, IEC 61000-4-4, and IEC 61000-4-5. 

Is there a protection IC or component from TI recommended for this purpose.

My interfaces are at typical 3.3V operating voltage.  

Thanks.

  • +1
    TI__Genius 10520 points

    Hi Kaveh, 

    We have a few recommendations for Ethernet and RS-232 interfaces.

    For Ethernet, there are a few options: ESDS30x (this is either a 2 or 4 channel, unidirectional device with a 3.6 working voltage), ESDS31x (this is also either a 2 or 4 channel, unidirectional device with a 3.6 working voltage), and ESD351 (1-channel, unidirectional device). 

    For RS-232, depending on whether the system is only seeing positive voltages or not, you can use the above suggestions. If the system is seeing both positive and negative voltages then bidirectional devices we recommend are: ESD341 (1-channel, bidirectional device), TSD05C (1-channel, bidirectional device), and ESDS552 (2-channel, bidirectional device). 

    Please let me know if you have any questions. 

    Best Regards, 

    McKenzie Eaker

  • 0 in reply to McKenzie Eaker
    Intellectual 585 points

    Thank you. I actually meant RS485 instead of RS232. Can you send me some recommendations for that as well. 

    I am also confused, when I look at the requirements in IEC 61000-4-5 level 1 (lowest level) for example, my device has to be protected against 0.5kV open circuit on a 1.2/50us curve and also 41.7A short circuit current on a 8/20us curve (based on 12ohms total load impedance in the standard). What you have suggested for example for ESD341, it just provides protection for IEC 61000-4-5 surge up to 5.4A short circuit current (on 8/20 µs curve) which seems too low compared with the requirements of the standard. 

    Can you please advise. 

  • +1 in reply to Kaveh Mohammad
    TI__Genius 10520 points

    Hi Kaveh, 

    We don't have many low voltage device options that will be able to protect against 0.5kV open circuit. The table below provides working voltage and surge voltage each device is able to protect up to. 

    Part number Working Voltage (V) IEC 61000-4-5 (A) Surge Voltage 
    ESDS302/ESDS304 3.6 12 504 V
    ESDS312/ESDS314 3.6 25 1.05 kV
    TSD05 5.5 60 2.52 kV
    TVS0500 5 43 1.806 kV

    The above specs for surge voltage are based on 42-Ohm impedance. If you are looking for 12-Ohm impedance, then the devices that will work would be TSD05 and TVS0500. The image below shows the comparison between impedances. 

    For RS-485, the main device we recommend is ESDS552. It is a 2-channel, bidirectional device with a working voltage of +/-12V and is able to support up to 1kV (using 42-Ohm impedance). 

    Please let me know if you have any questions. 

    Best Regards, 

    McKenzie 

  • 0 in reply to McKenzie Eaker
    Intellectual 585 points

    Thanks. I have decided to use TVS0500 for my ethernet based on your recommendation.

    I can see there is a requirement for line to ground which is 41.7A short circuit current on a 8/20us curve. But there is also a requirement for line to line which is a short circuit 0.25kA. How do we tackle this? Should we put also a TVS between each two lines of the ethernet port or TVS0500 we added between each node and the ground will do the protection? What is the practice in this case?

    Please advise.

  • +1 in reply to Kaveh Mohammad
    TI__Genius 10520 points

    Hi Kaveh, 

    Unfortunately, we don't have anything in our portfolio to meet the 0.25kA requirement for line to line short circuit. Looking at the image below, it seems like the device would have to withstand up to 3kV open circuit (250A short circuit) at 12-Ohm impedance. 

    I would suggest looking into a SMA/SMB/SMC protection device. Also, for this application, is the ESD protection device being placed at the RJ45 connector for Ethernet or is it being placed after the transformer? 

    Best, 

    McKenzie

  • 0 in reply to McKenzie Eaker
    Intellectual 585 points

    Protection device are after the transformer or the internal magnet of the ethernet. 

    In general I have not seen TVS protection devices to be implemented between lines. They are typically placed only between each line and the ground. 

  • +1 in reply to Kaveh Mohammad
    TI__Genius 10520 points

    Hi Kaveh, 

    The below image shows one of the ways we use a 4-channel protection diode. 

    This diagram can also change whether you are using a 2-channel or 1-channel device. If it is 2-channel, then placing one diode between TD+ and TD- and the other between RD+ and RD-. For 1-channel, this would require using 4 devices with one connected to each line. 

    Best, 

    McKenzie